KILLEEN, Texas (CBS) — A Calumet City soldier was the main suspect in the murder of fellow soldier Vanessa Guillen, CBS 2 has learned.

Aaron David Robinson, 20, died by suicide Wednesday morning as investigators were closing in.

The Calumet City native entered the Army in October 2017 and was a combat engineer.

Guillen’s family said she planned to file a harassment complaint against Robinson, said Robinson became enraged when she told him and killed her a day before she planned to do it.

Dismembered human remains believed to be Guillen’s were found in a shallow grave about 30 miles east of the Fort Hood base this week.

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Military investigators said Guillen was bludgeoned with a hammer.

Robinson’s estranged wife has been arrested for her alleged involvement in the case. Cecily Aguilar, 22, a civilian, told investigators Robinson asked her to help hide a body.

Aguilar has been charged with one count of conspiracy to tamper with evidence.